Upper-twin-peak quasiperiodic oscillation in x-ray binaries and the energy from tidal circularization of relativistic orbits

TL;DR

This paper investigates how tidal forces acting on plasma clumps in accretion disks around neutron stars can explain the observed properties of high-frequency quasiperiodic oscillations, linking gravitational effects to observable X-ray signals.

Contribution

It introduces a model where tidal circularization of relativistic orbits accounts for the coherence and amplitude of upper HF QPOs in neutron star X-ray binaries, providing new insights into strong gravity effects.

Findings

Tidal forces can reproduce the observed coherence of upper HF QPOs.

Energy released during orbit circularization matches observed modulation amplitudes.

Relativistic boosting enhances the QPO signal, consistent with observations.

Abstract

High frequency quasiperiodic oscillations (HF QPOs) detected in the power spectra of low mass x-ray binaries (LMXBs) could unveil the fingerprints of gravitation in strong field regime. Using the energy-momentum relation we calculate the energy a clump of plasma orbiting in the accretion disk releases during circularization of its slightly eccentric relativistic orbit. Following previous works, we highlight the strong tidal force as mechanism to dissipate such energy. We show that tides acting on the clump are able to reproduce the observed coherence of the upper HF QPO seen in LMXBs with a neutron star (NS). The quantity of energy released by the clump and relativistic boosting might give a modulation amplitude in agreement with that observed in the upper HF QPO. Both the amplitude and coherence of the upper HF QPO in NS LMXBs could allow us to disclose, for the first time, the tidal circularization of relativistic orbits occurring around a neutron star.